The present invention generally relates to the field of energy conversion and more particularly, is directed to a method and apparatus for efficient and practical conversion of mechanical energy into electrical energy. Conversion of mechanical into electrical energy has many applications from electronic measurements and analysis to power generation. The present invention greatly advances society's goal of using all forms of energy sources, especially renewable sources, to meet the energy needs of mankind.
While a preferred embodiment of the present invention will be described with reference to mechanical energy derived from wind, the invention has application to many sources of energy where the energy is in the form of a moving fluid or a fluid that is stationary and impedes movement.
As used herein, the term “fluid” includes such substances as air, liquids and gases. The phrase “energy conversion” and similar terms are used herein in accordance with the well known law of conservation of energy. In summary, this law states that the total amount of energy in an isolated system remains constant. Thus, energy can not be created or destroyed, but can only be changed, i.e., converted, from one form into another.
Wind turbines are well known in the prior art as a way to convert wind energy into mechanical energy and then to convert the mechanical energy into electrical energy. Conventional wind turbines typically come in two types based on the axis in which the turbine rotates.
Horizontal axis wind turbines include a main rotor shaft, a gear box, an electrical generator of some type and in many cases, a solid state power converter. The turbine is mounted on top of a tall tower with the main rotor shaft pointed into the wind. Small horizontal axis wind turbines are pointed by a simple wind vane, while the pointing of large turbines typically is performed by a wind direction sensor coupled to a closed loop controlled servo drive motor.
Almost all horizontal axis wind turbines are equipped with three rotor blades. The individual rotor blade lengths may range from 65 to 130 ft or more and rotate from 10 to 25 rpm. As known in the prior art, this rather complex and relatively heavy equipment package usually is installed on top of tubular towers ranging in height from 150 to 300 feet.
Modern wind turbines also are equipped with a high wind shut down feature, or governor, to prevent catastrophic damage due to unexpectedly high wind velocities. The wind shut down velocity typically is between 25 and 30 meters per second (approximately 56 to 67 miles per hour).
The technical problems associated with horizontal axis wind turbines include, but are not limited to:                a) Horizontal axis wind turbines cannot efficiently operate in turbulent wind conditions encountered close to the ground. Horizontal turbines require laminar wind conditions to operate efficiently;        b) The typically large dimensions of tall towers and associated blades are difficult and expensive to handle and transport. The transportation and handling costs can range between 30% to 40% of basic hardware cost, depending on the topography of the installation site;        c) Tall horizontal wind turbines are extremely expensive to install, particularly in topographically challenging and remote terrains;        d) Massive tower foundation construction is required to support tall horizontal wind turbine structures;        e) Maintenance of tall horizontal wind turbines is very expensive as evident from an entirely new industry that has developed to exploit these high cost;        f) Tall horizontal wind turbines directly and detrimentally affect military and commercial air traffic control and safety based on their interference with radar technology;        g) Environmental groups oppose horizontal wind turbines due to their adverse and detrimental impact on the population and migration of birds;        h) Tall horizontal wind turbines are obtrusively visible across large areas, disrupting the appearance of the landscape and in numerous cases causing local opposition to their construction;        i) Downwind variants of horizontal wind turbines are susceptible to fatigue and structural failure due to turbulence; and        j) Cyclic stresses, fatigue and vibration are a major cause of failure of horizontal axis wind turbines. That is the reason why 15% or more of them may be out of service at any one time in major installations.        
Vertical axis wind turbines rotate on a vertical rotor shaft and are less commonly used for various reasons. The technical problems associated with vertical axis wind turbines typically include, but are not limited to, the following:                a) A vertical axis wind turbine is about 50% less efficient than a horizontal wind turbine due to higher blade drag while rotating in the wind;        b) As vertical axis turbines can not be packaged and installed on towers, they are not able to take advantage of stronger, more laminar, wind conditions at higher elevations;        c) Like their horizontal axis counterparts, vertical axis turbines cannot efficiently operate in turbulent wind conditions typically encountered near the ground. They require laminar wind conditions to operate efficiently;        d) Some vertical axis wind turbines have a high starting torque and require auxiliary energy sources to get started; and        e) Some vertical axis wind turbines require guy cables to hold them in place. These guy cables add additional load to the bottom bearing of the turbine. This is particularly so in the event of strong wind gusts as the bearing absorbs the total weight of the turbine rotor. Superstructures may be required to support and hold the top bearing in place.        
In many regions of the world, wind is readily available and in abundant supply. The fact that wind is eco-friendly, and renewable, makes it an ideal energy source. Thus, while wind turbines have their limitations as described above, they remain an important way of converting mechanical energy into electrical energy. However, wind turbines have further limitations imposed by the laws of physics that can not be easily overcome.
For example, Betz's law states that the maximum power P that can be extracted by any wind turbine from the free flow of wind is given by the following equation.P=½αρπr2v3                 Where:        P=Power (watts);        α=Efficiency factor based on the design of the wind turbine as defined by Betz's law;        ρ=Mass density of air (kg/m3);        r=Radius of the wind turbine blade path (m); and        v=Velocity of the wind (m/s);        
Betz's law states that the efficiency factor α can not exceed 0.59 regardless of the type and design of the wind turbine. Thus, a typical horizontal wind turbine with a turbine blade radius of r=0.02125 m, and a very conservative Betz factor of α=0.17, is potentially capable of producing 12 watts at a wind velocity of 43 m/s or 96 mph, assuming a mass density of air at sea level of ρ=1.225 kg/m3.
Thus, the number and severity of the above noted limitations and deficiencies of traditional wind turbines make their use less than ideal in many situations. Moreover, the use of traditional wind turbines is completely unsuited for some applications. Thus, other forms of energy conversion are known in the prior art.
Examples of alternative forms of energy conversion include (1) batteries, where energy stored in chemical form is converted into electrical energy through a chemical reaction; (2) fuel cells, where a chemical reaction between hydrogen and oxygen atoms is converted into electrical energy; (3) electric generators where mechanical energy in the form of a prime mover is converted into electrical energy; and (4) solar energy where radiant light from the sun is converted into electrical energy.
While each of these alternative forms of energy conversion has advantages in particular applications, they also have disadvantages in other applications. The advantages have chiefly to do with their ability to used the energy source at hand for conversion into electrical energy. The disadvantages have chiefly to do with the amount of energy that can be converted, physical size and cost considerations.
While batteries can be made small in size and at low cost, they are limited in the amount of electrical energy that can be converted from their chemical reaction. Depending on their design, fuel cells can operate at higher sustained energy levels and for longer periods of time than batteries but are very expensive to manufacture. Prior art electric generators can be designed to operate at high energy levels but also are expensive, physically large in size and required a largest amount of source energy. Prior art approaches to solar energy conversion suffer from low conversion efficiency and, in many cases, the lack of a continuous supply of solar energy.
Thus, there remains a need in the art for a method and apparatus for converting mechanical energy into electrical energy which addresses the above noted disadvantages and deficiencies associated with conventional energy conversion methods and apparatuses.